I scanned about 5,800 negatives in Vuescan with my Minolta Scan Elite II, using a fixed exposure for each film roll.
Just to explain my workflow: My intention was to convert the film rolls in Negadoctor by picking individual features where they apply (see * below) in order to create a general profile of the film roll’s features. Then I would merely adapt the “print properties” (apart from “paper grade”) of the individual images.
So far, so good.
Unfortunately, in the DNG files, the scanner produces some very dark pixels in the green channel, sometimes even a kind of weak white-noise pattern in the RAW shadows. In many cases, I wouldn’t mind, because these pixels would disappear in the highlights range of the converted image. However, when sampling D max with the color picker, these extreme shadows are counted as the “densest” areas of the film, thus creating a higher D max and pushing the rest of the image into the shadows.
If such a “faulty” D max is kept in place, you can counteract it with the print properties sliders on paper black and print exposure (including paper gloss) - but only within the “distorted” spectrum of the nonlinear curve that D max imposes on the overall picture - or via the “paper grade (gamma)” slider - which may impose even more nonlinear distortion.
I feel really insecure about whether a D max is really based on a “correct” value or just a distortion or “outlier” - particularly since this value is very important for the entire character of the image. Also, this potentially affects a lot of scans with high loading times per image.
Of course, there is a default value of D max in Negadoctor, but there is no real standard range of D max, since it depends on many factors (e.g. exposure of the scan; film stock). In one forum discussion, Aurélien highlights an aggressively low D max of one user, while he uses a low one himself in a Youtube video.
- I could try to find these faulty pixels and exclude them from the color picker’s sampling area - exhausting.
- I could also work with the histogram - with all corrections in the later tabs disabled - could be imprecise
- I tried using a blurring filter - but this also “pushes down” the correct highlights in the RAW
- De-noising (on the RAW, before Negadoctor) does not seem to affect those extremely dark pixel values, but rather, the “correct” ones above them.
My question:
Can you see any better solution to this?
Is there some kind of low pass filter that specifically excludes (brightens) such outliers in the RAW (in the pipeline before Negadoctor) without affecting the “correct” values too (as a tone curve would)?
I could add sample DNG files, but each is 232MB in size.
*footnote on sampling sources: film base from test strip, D max [and paper grade] from the brightest photograph, scan exposure bias by comparing the values of several images containing “real” black, color corrections from images with a neutral light source - if possible